Termination for resistor and method of making the same

ABSTRACT

A method of making a resistor termination comprising the steps of applying to the surface of a substrate and firing a mixture of glass frit and particles of a compound taken from the group consisting of ruthenium oxide, iridium oxide, and rhodium oxide and mixtures thereof, until the compound dissociates to form and sinter the metal. The mixture is fired at a temperature of at least 900*C and preferably at 1,150*C in a reducing or nonoxidizing atmosphere such as that provided by nitrogen. When cooled there is provided a glass film with metal particles therein strongly bonded to the substrate.

United States Patent 11 1 MacKenzie et al.

[4 1 Oct. 21, 1975 1 TERMINATION FOR RESISTOR AND METHOD OF MAKING THE SAME [75] Inventors: George D. MacKenzie, Maple Glen,

Pa.; Michael G. Noblett, Ventnor, NJ.

[73] Assignee: TRW, Inc., Cleveland, Ohio [22] Filed: Aug. 16, 1973 [21] Appl. No.: 388,734

[52] US. Cl. 428/426; 428/457; 427/101; 427/376; 427/377; 427/383; 252/514; 252/518 Primary Examiner-Michael F. Esposito Attorney, Agent, or Firm.lacob Trachtman [57] ABSTRACT A method of making a resistor termination comprising the steps of applying to the surface of a substrate and firing a mixture of glass frit and particles of a compound taken from the group consisting of ruthenium oxide, iridium oxide, and rhodium oxide and mixtures thereof, until the compound dissociates to form and sinter the metal. The mixture is fired at a temperature of at least 900C and preferably at 1,150C in a reducing or non-oxidizing atmosphere such as that provided by nitrogen. When cooled there is provided a glass film with metal particles therein strongly bonded to the substrate.

7 Claims, 1 Drawing Figure /4- TERM/NAT/O/V (METAL 61. A25) /6- RES/STANCE FILM /2- cyan/c TERMINATION, FOR RESISTOR AND ivniriioo or MAKING THE SAME The present invention relates to.a method of making a resistor termination and the termination produced thereby, and more particularly to a methodof making a conductive termination for a vitreous'en'amel resistor.

Vitreous enamel resistors include 'a substrate having on a surface thereof, a film of glass and particlesof'a' metal borides, and nitrides, have been fired in .non-

oxidizing environments. When the resistor is cooled,

the glass solidifies to form the glass film with the conductive particles therein.

in order to provide an electrical connection to the resistor it is desirable to provide on the substrate at each end of the resistance film a conductive termination. Heretofore, the termination generally used for resistors of the type produced in a non-oxidizing atmosphere, was a film of a metal, such as nickel or copper. However, it has been found that such metal film terminations are not suitable for many vitreous enamel resistance products.

Therefore, it is an object of the present invention to provide a novel method of making a termination for a vitreous enamel resistor.

It is another object of the present invention to provide a novel termination for a vitreous enamel resistor.

It is still another object of the present invention to provide a novel resistor termination.

These objects are achieved by applying to a substrate a mixture of a glass frit and particles of ruthenium oxide, iridium oxide, rhodium oxide or mixtures thereof. The substrate and coating are then heated in a nitrogen atmosphere at a temperature at which the glass frit melts and the metal oxide dissociates to the metal form and the metal sinters to a dense film which is strongly bonded to the substrate.

The invention accordingly comprises the several steps and the relation of one or more of such steps with respect to each of the others, and the composition possessing the features, properties, and the relation of constitutents which are exemplified in the following detailed disclosure, and the scope of the invention will be indicated in the claims.

For a fuller understanding of the nature and objects of the invention, reference should be had to the following detailed description taken in connection with the accompanying drawing in which:

The FIGURE of the drawing is a sectional view of a resistor having the termination of the present invention.

Referring to the drawing there is shown a resistor 10 which comprises a substrate 12 of an electrical insulating material, such as a ceramic, a termination film 14 on a surface of the substrate 12, and a resistance film 16 on the surface of the substrate and contacting the termination film 14. The resistance film 16 is a vitreous enamel resistance film which comprises a film of glass 2 having particles of a conductive material embedded therein and dispersedtherethroughout. The conductive material may be a'nyof the well known materials used in vitreous enamelresistors.

The termination film 14,comprises a layer of glass having particles of either ruthenium, iridium, rhodium or mixtures thereof, embedded'in and dispersed therethroughout. The amount of the metal present in the termination film is preferably between 60% and 92% by volume or 79% to 99% by weight. The glass may be any glass having a suitable melting temperature, i.e., a melting temperature below that of the metal. The glasses most preferable are the borosilicate glasses, such as lead borosilicate, bismuth, cadmium, barium, calcium, or other alkaline earth borosilicates. If desired, up to 5% of the metal can be replaced by copper particles to improve the solderability of the termination film 14.

' To make the termination film 14, a termination material is first formed. The termination material comprises a mixture of a glass frit and particles of either ruthenium oxide, iridium oxide, rhodium oxide or mixtures of the oxides. The amount of the oxide included is dependent on the volume percent of the metal desired in I the termination film. The following table shows the amount of the oxide by weight percent needed to achieve 60% and 92% by volume of the metal .in the termination film. 1

The glass frit and the metal oxide particles are thoroughly mixed together, such as by milling, in a suitable vehicle, such as butyl carbital acetate, a mixture of butyl carbitol acetate and toluol or any well known screening medium. The viscosity of the mixture is then adjusted for the desired manner of applying the material either by adding or removing some of the vehicle medium. If copper is to be included in the termination film, it is included in the termination material either as copper particles or copper oxide particles.

The termination material is then applied to the substrate 12 by any desired technique, such as brushing, dipping, spraying or screen stencil application. The coated film is then preferably dried, such as by heating at a low temperature, such as C for about 10 minutes. Next, the film is heated at a higher temperature, about 400C or higher, to burn off the vehicle. Finally, the film is fired at a temperature at which the glass melts, generally at least 900C and preferably l,l50C, in an atmosphere, such as nitrogen, which allows dissociation of the metal oxide and sintering of the metal thus formed. After the termination film 14 is applied to the substrate 12, the vitreous enamel resistance film 16 can be applied to the substrate in the manner well known in the art.

The following table provides test results for resistors utilizing terminations produced in accordance with the present invention.

Not Tested The change in resistance shown in the Table is for the application of 50 watts per square for a period of 100 hours. The small change in resistance from the power loading and the low value of current noise for the resistors indicate good electrical continuity between the resistor and the termination film.

The present invention may be carried out and embodied in other specific forms without departing from the spirit or essential attributes thereof, and, accordingly, references should be made to the appended claims, rather than the foregoing specification as indicating the scope of the invention.

What is claimed is:

l. A method of making a termination for refractory metal glaze resistors comprising the steps of:

a. applying to the surface of a substrate a mixture of a glass frit and particles of a compound taken from the group consisting of ruthenium oxide, iridium oxide, rhodium oxide, and mixtures thereof, the metal oxide particles being present in the amount of 79% to 99% by weight and b. firing the mixture at a temperature of at least 900C in a non-oxidizing atmosphere until the compound dissociates to formand sinter the metal.

2. The method in accordance with claim 1 in which the mixture is fired at a temperature of at least 900C in a nitrogen atmosphere.

3. The method in accordance with claim 1 in which the mixture is fired at a temperature of between l,lOOC to l,l50C.

4. The method in accordance with claim 2 in which the metal oxide particles are present in the mixture, such that the amount of metal in the termination is between and 92% by volume.

5. The method in accordance with claim 4 in which copper particles are present in the mixture and in which of the metal oxide and copper particles no greater than 5% are of the copper particles.

6. The method in accordance with claim 5 in which the copper particles include particles of copper and copper oxide.

7. A termination film for an electrical refractory metal glaze resistor consisting of a glass film bonded to the surface of an insulating substrate, and particles of metal from the group consisting of ruthenium, iridium and rhodium, and mixtures thereof, embedded within and dispersed throughout the glass film, the metal particles being present in the amount of 60% to 92% by volume. 

1. A METHOD OF MAKING A TERMINATION FOR REFRACTORY METAL GLAZE RESISTORS COMPRISING THE STEPS OF: A. APPLYING TO THE SURFACE OF A SUBSTRATE A MIXTURE OF A GLASS FRIT AND PARTICLES OF A COMPOUND TAKEN FROM THE GROUP CONSISTING OF RUTHENIUM OXIDE, IRIDIUM OXIDE, RHODIUM OXIDE, AND MIXTURES THEREOF, THE METAL OXIDE PARTICLES BEING PRESENT IN THE AMOUNT OF 79% BY WEIGHT AND B. FIRING THE MIXTURE AT A TEMPERATURE OF AT LEAST 900*C IN
 2. The method in accordance with claim 1 in which the mixture is fired at a temperature of at least 900*C in a nitrogen atmosphere.
 3. The method in accordance with claim 1 in which the mixture is fired at a temperature of between 1,100*C to 1,150*C.
 4. The method in accordance with claim 2 in which the metal oxide particles are present in the mixture, such that the amount of metal in the termination is between 60% and 92% by volume.
 5. The method in accordance with claim 4 in which copper particles are present in the mixture and in which of the metal oxide and copper particles no greater than 5% are of the copper particles.
 6. The method in accordance with claim 5 in which the copper particles include particles of copper and copper oxide.
 7. A termination film for an electrical refractory metal glaze resistor consisting of a glass film bonded to the surface of an insulating substrate, and particles of metal from the group consisting of ruthenium, iridium and rhodium, and mixtures thereof, embedded within and dispersed throughout the glass film, the metal particles being present in the amount of 60% to 92% by volume. 